The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
For example, spare parts that are no longer so easy to find on the market are often needed for motor vehicles. A typical example of this is the case of spare parts for classic cars. The injection molds from which the articles were earlier produced frequently no longer exist. The shape of the articles is generally known, however; it can be determined by scanning or other methods, particularly if there is an old, possibly also no longer serviceable article to hand. Once the shape is known it is possible to produce the article by 3-dimensional printing methods. These are usually printed layer by layer. As a result the surface of the article printed in this way is decidedly too rough; it has a poor surface quality. In particular it is not smooth.
The term “article with a polymer surface” is here taken to mean that the article is composed at least partially of plastic, or more precisely at least a part of the surface is composed of plastic. It is this part which exhibits the excessive roughness that needs to be reduced. The article may have a metal core, for example, on which the plastic material is applied.
DE 11 2014 002 879 T5 discloses a method in which a liquid solvent is first applied to the surface by immersing the article in the liquid solvent, for example also acetone; this can be done at room temperature. The solvent is removed again by suction extraction, that is to say by applying a vacuum. The suction extraction is preferably performed at higher temperature in a vacuum oven. The vacuum used for this ranges from 100 to 250 Torr. 250 Torr corresponds approximately to ⅓ of the normal atmospheric pressure or approximately 33 KPa. The application of a layer of gel is also described. The gel layer is allowed to set in order to smooth at least a part of the surface whilst reducing the roughness.
U.S. Patent Application No. 2014/0264294 A1 discloses the surface treatment of articles that have been produced by the 3D method.
Acetone C3H6O is the common name for propanone or also dimethyl ketone, the simplest ketone. Acetone is a colorless liquid and is used, among other things, as an aprotic solvent. Acetone is known to be a very good solvent. It is used for cleaning in various branches of industry. Its characteristic structural feature is the carbonyl group, which is bonded with two methyl groups. The boiling point is 56° C., the vapor pressure is 233 kPa at 20° C. In higher concentrations acetone forms an explosive mixture with air. At normal air pressure the substance ignites at approximately 56° C.
JP 000H05239240 A1 teaches a method of surface treatment. CN 103192524 A discloses a method and a device using a system of baths.
3D-printed plastic articles, which are the articles mainly involved here, can also be smoothed, for example, by sand blasting or grinding. These do not allow the treatment of constrictions, undercuts and other problem points, however, at any rate to adequate quality standards. Small details important to the article may be lost in the treatment process. The outcome depends on the skill of the person performing the treatment. Treatment can usually only be performed manually and such treatment is costly. In the treatment process often too much material is removed locally, and often too little, so that the overall quality is unsatisfactory.
Instead of sand, yet other blasting abrasives may be used, for example CO2 ice particles or other particles, such as glass beads, for example. Here similar problems arise to those described above for sand blasting.
One common method is smoothing of the surface through treatment with acetone. A distinction is made here between a cold and a hot method. It is known that acetone dissolves or at least partially dissolves a large number of plastics, for example ABS In the cold method the printed parts are put into a vessel, the bottom of which is covered with a small quantity of acetone. The vessel is closed. The acetone passes increasingly into the gaseous state and dissolves approximately 2 μm from the surface of the printed article. Such stripping by means of vaporous acetone typically takes 3 hours. Great care has to be taken to see that an explosion does not occur.
The hot method carries an even greater risk of explosion than the cold method. In the hot method heat is delivered, thereby actively bringing the acetone into the gaseous state. Temperatures of 60° C. and above are applied. The process thereby runs relatively quickly but has to be used with great caution owing to the increased risk of explosion